The present invention relates to production of olefin oxides (epoxides), particularly to processes for forming the epoxides via the corresponding halohydrin processes.
Halohydrin processes for the production of epoxides, including ethylene oxide, propylene oxide, butylene oxide, epichlorohydrin, and the like, advantageously involve the reaction of chlorine (or other halogen or hypohalite) with the corresponding piefin (ethylene, propylene, butene, allyl chloride, respectively) in aqueous solution to produce an intermediate halohydrin. The halohydrin may then be reacted with a base to produce the desired epoxide and brine. The epoxide is advantageously stripped from the brine and is optionally separated from various byproducts. The brine is optionally treated for removal of residual impurities. There are numerous variations on each of these reactions.
A particularly advantageous variation of the halohydrin process is the use of low-chlorides aqueous hypochlorous acid (HOCI), in place of chlorine gas, for reacting with the piefin. This HOCI variation is advantageous because of a resulting increased selectivity for the desired epoxides. Chloride ions are preferably in low concentrations because they contribute to the production of undesirable chlorinated organic byproducts such as di- and trichlorides and they accelerate decomposition of HOCI to chlorates. A problem with the halohydrin process, however, is that there is a significant amount of waste water discharge from the process. For example, in the production of one kilogram (kg) of propylene oxide product, typically greater than 40 kg of water containing various undesirable organic byproducts and about 5-10 weight percent (wt-%) sodium chloride salt or 5-6 wt-% calcium chloride salt is generated. These aqueous waste streams are of little or no commercial value and therefore must be discharged after suitable treatment. See K. H. Simmrock, "Compare Propylene Oxide Routes", 57 Hydrocarbon Processing 109-10 (November 1978).
Therefore, there is a need for a low chlorides HOCI process for producing epoxides that substantially reduces or eliminates waste water discharge. The present invention is a method for producing epoxides comprising the steps:
(a) forming a low chlorides aqueous hypochlorous acid solution; PA1 (b) contacting the low chlorides aqueous hypochlorous acid solution with at least one unsaturated organic compound to form an aqueous organic product comprising at least olefin chlorohydrin, wherein the unsaturated organic compound contains from 2 to about 10 carbon atoms and is selected from the group consisting of substituted and unsubstituted olefins and cyclic olefins, the substituted olefins having substituents selected from the group consisting of an alkyl radical, a phenyl radical, and an alkylphenyl radical, each radical being independently either unsubstituted or substituted; PA1 (c) contacting at least the olefin chlorohydrin with an aqueous alkali metal hydroxide to form an aqueous salt solution product containing at least epoxide; and PA1 (d) isolating the epoxide from the aqueous salt solution; PA1 (a) contacting an aqueous alkali metal hydroxide solution with chlorine to produce an aqueous alkali metal hypochlorite solution; PA1 (b) contacting droplets of the aqueous alkali metal hypochlorite solution with chlorine gas to produce aqueous hypochlorous acid; PA1 (c) vaporizing at least about 30 weight percent of the aqueous hypochlorous acid to produce a vapor phase and a liquid phase, the vapor phase comprising chlorine, water vapor, hypochlorous acid, and dichlorine monoxide, the liquid phase comprising hypochlorous acid in an aqueous salt solution; PA1 (d) distilling the liquid phase using a vapor stripping stream containing at least about 20 mole percent chlorine to strip vapor phase hypochlorous acid and dichlorine monoxide from the aqueous salt solution; and PA1 (e) absorbing the vapor phase hypochlorous acid and dichlorine monoxide from both Steps (c) and (d)into water. PA1 (a) contacting an aqueous alkali metal hydroxide solution with chlorine to produce an aqueous alkali metal hypochlorite solution; PA1 (b) contacting droplets of the aqueous alkali metal hypochlorite solution with chlorine gas to produce hypochlorous acid in an aqueous salt solution; PA1 (c) extracting the hypochlorous acid from the aqueous salt solution using an organic solvent; PA1 (d) stripping the hypochlorous acid from the organic solvent using a non-reactive gas; and PA1 (e) absorbing the stripped hypochlorous acid into water.
wherein water is recovered from the product of at least Step (b) and recycled into Step (a) for use in forming the low chlorides aqueous hypochlorous acid solution. Optionally, water in the form of a concentrated sodium chloride brine from Step (a) and Step (d) may be used as feed to an electrochemical cell for production of chlorine and caustic which, in turn, may be use in the method of this invention.
This method may be run continuously, inhibits formation of chlorinated byproducts, and substantially reduces or eliminates waste water discharge by, first, recycling water internally after Step (b) and, second, generating a concentrated brine solution in Step (a) and Step (d) that is useful in other processes such as electrochemical production of chlorine and caustic.